24 THE BLOOD. 



In addition to the organic nitrogenized principles which we have described, some 

 authors recognize a substance called paraglobuline, or fibrinoplastic matter, and fibrino- 

 genic matter. These are supposed to be factors of fibrin, which come together in the 

 coagulation of the blood. They will be considered in connection with the theories of 

 coagulation. The so-called albuminates of soda and potassa have not been positively 

 established as proximate principles. 



Coagulation of the Blood. 



The remarkable property in the blood of spontaneous coagulation has been recog- 

 nized almost as far back as we can look into the history of physiology ; and, since the 

 discovery of the circulation, there have been few subjects connected with the physiology 

 of the blood which have excited more universal interest ; but the ideas with regard to 

 the cause of this phenomenon were for a long time entirely speculative. The first defi- 

 nite experiments upon this subject were performed by Malpighi. He was followed by 

 Borelli, Euysch, and a host of others, who hold conspicuous places in the history of our 

 science, among whom may be mentioned Hunter, Hewson, Mtiller, Thackrah, J. Davy, 

 Magendie, JSTasse, and Dumas. Although much labor has been expended OD this subject, 

 the final cause of coagulation is by no means definitely settled. 



The blood retains its fluidity while it remains in the vessels and circulation is not 

 interfered with. It is then composed, as we have seen, of a clear plasma, holding cor- 

 puscles in suspension. Shortly after the circulation is interrupted, or after blood is 

 drawn from the vessels, it coagulates or " sets " into a jelly-like mass. In a few hours, 

 we find that contraction has taken place, and a clear, straw-colored fluid has been ex- 

 pressed, the blood thus separating into a solid portion, the crassamentum, or clot, and a 

 liquid, which is called serum. The ssrnm contains all the elements of the blood except 

 the corpuscles and fibrin, which together form the clot. Fibrin is one of the products 

 of decomposition of plasmine. Coagulation takes place in the blood of all animals, com- 

 mencing a variable time after its removal from the vessels. In the human subject, ac- 

 cording to Nasse, when the blood is received into a moderately-deep, smooth vessel, the 

 phenomena of coagulation present themselves in the following order : 



First, a gelatinous pellicle forms on the surface, which occurs in from one minute and 

 forty -five seconds to six minutes ; in from two to seven minutes, a gelatinous layer has 

 formed on the sides of the vessel ; and the whole mass becomes of a jelly-like consistence, in 

 from seven to sixteen minutes. Contraction then begins, and, if we watch the surface 

 of the clot, we see little drops of clear serum making their appearance. This fluid in- 

 creases in quantity, and, in from ten to twelve hours, separation is complete. The clot, 

 which is heavier, sinks to the bottom of the vessel, unless it contain bubbles of gas or 

 the surface be very concave. In most of the warm-blooded animals, the blood coagulates 

 more rapidly than in man. It is particularly rapid in the class of birds, in some of which 

 it takes place almost instantaneously. Observations have shown that coagulation is more 

 rapid in arterial than in venous blood. In the former, the proportion of fibrin formed is 

 notably greater, and, as we have seen, the characters of the fibrin are somewhat differ- 

 ent. A solution of chloride of sodium dissolves the fibrin of venous blood, but does not 

 dissolve the fibrin of an arterial clot. 



The relative proportions of the serum and clot are very variable, unless we include in 

 our estimate of the serum that portion which is retained between the meshes of the coag- 

 ulated mass. As the clot is composed of corpuscles and fibrin, and as these in their 

 moist state represent in general terms about one-half of the blood, it may be stated 

 that, after coagulation, the actual proportions of the clot and serum are about equal. 

 If we take simply the serum which separates spontaneously, we have a large quantity 

 when the clot is densely contracted, and a very small quantity when it is loose and 

 soft. Usually, the clot retains about one-fifth of the serum. 



